ML20209C017

Forwards Special Rept 99-01 Re Fifteenth Year Inservice Containment Bldg Tendon Surveillance Failure.Observed Voids in Sheathing Filler Grease Do Not Indicate Degradation of post-tensioning Sys,Based on Encl Evaluation

ML20209C017
Person / Time
Site:	Callaway
Issue date:	06/28/1999
From:	Taylor M UNION ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ULNRC-4058, NUDOCS 9907090008
Download: ML20209C017 (6)

Text

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• Union Eltctric Yo Dox 620 i , . Callaway Plant Fulton, MO 65251 June 28,1999 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop Pl-137 Washington, DC 20555-0001 gf/, ULNRC-4058 N Gentlemen:

UE DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT I FACILITY OPERATING LICENSE NPF-30 SPECIAL REPORT 99-01 FIFTEENTH YEAR INSERVICE CONTAINMENT BUILDING TENDON SURVEILLANCE FAILURE The enclosed Special Report is an engineering evaluation submitted to satisfy Final Safety Analysis Report (FSAR) Section 16.6.1.2.b and Technical Specification (T/S)

Section 6.9.2.

During the fifteenth year surveillance on June 14,1999, the acceptance criteria of the FSAR 16.6.1.2.l(d).2 was exceeded. This was due to the net refill volume of the sheathing filler grease exceeding 5% of the net duct volume for two tendons.

Based on the enclosed engineering evaluation, the observed voids in the sheathing filler grease do not indicate degradation of the post-tensioning system. The structural l integrity of the containment building structure is assured. I

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M. E. Taylor Asx Dp Manag r, Nuc car Engineering

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MET /DSH/DLB crp f Enclosure 9907090000 990628 PDR ADOCK 05000483 p PDR a subsidiary of Amoren Corporation

ULNRC-4058 Page 2 j i

cc: U. S. Nuclear Regulatory Commission (Original and I copy) l Attn: Document Control Desk l Mail Stop Pl-137  !

Washington, DC 20555-0001 l Mr. Ellis W. Merschoff i Regional Administrator l U.S. Nuclear Regulatory Commission I Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission l 8201 NRC Road Steedman, MO 65077 Mr. Melvin K. Gray (2 copies)

Licensing Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 13E16 Washington, DC 20555-2738 Manager, Electric Department Missouri Public Service Commission  ;

PO Box 360 Jefferson City, MO 65102 Deputy Director Department of Natural Resources PO Box 176 Jefferson City, MO 65102 i

Superintendent, Licensing Wolf Creek Nuclear Operating Corporation PO Box 411 Burlington, KS 66839  ;

ULNRC-4058

', Page 3 bec: G. L. Randolph J. V. Laux/G. A. Hughes A. C. Passwater/D. E. Shafer (470)

M. L. Orr (470) NSRB H. D. Bono D. H. Zimmerman w/a H. J. Potter w/a E210.0001 A160.0761 MET Chrono l

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SPECIAI. REPORT 99-01 l l

EVALUATION OF TIIE FIFTEENTII YEAR INSERVICE TENDON SURVEILLANCE i AND EXTEPIOR CONCRETE INSPECTION FOR TIIE

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CALLAWAY PLANT CONTAINMENT HUILDING j l

TENDON SIIEATlilNG FILLER GREASE VOIDS l GREATER THAN 5% OF NET SHEATHING DUCT VOLUME REFERENCE TECHNICAL SPECIFICATION SECTIONS 4.6.1.1.e AND 6.8.5.c AND THE FINAL SAFETY ANALYSIS REPORT (FSAR) SECTION 16.6.1.2.l(d). 2 GREASE VOID FINDINGS On June 14,1999, it was discovered that the net refill volume of the sheathing filler grease exceeded 5%

of the net duct volume for two tendons. This void condition did not meet the acceptance criteria in the FSAR Section 16.61.2.1(d). 2.

The FSAR requires verification of operability of the sheathing filler material, by assuring the " amount of grease replaced does not exceed 5% of the net duct volume, when injected at110% of the specified installation pressure." Since a void greater than 5% was discovered after filling, restoration of the tendon sheathing filler grease and the FSAR action statement 16.6.1.2.b was immediately satisfied with the exception of the Special Report. The NRC staff concurred with this position in a meeting on the same subject for the first year tendon surveillance on July 19,1985.

This condition was documented in the surveillance contractor's non-conformance reports, N667-006 and N667-008 and AmerenUE's SOS /NMR 99-1119.

The measured voids are:

Tendon Surveillance Greasina Summary Tendon Percent Void 40CB 6.0 6AC

5.7 BACKGROUND

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The Callaway containment building is a post-tensioned, reinforced concrete structure comprised of a vertical cylinder with a hemispherical dome roof and is supported by a reinforced concrete slab. A continuous access gallery is provided beneath the foundation slab for inspection of the vertical tendons.

Three concrete buttresses are provided for anchorage of the horizontal tendons. Anchorages are  !

designed such that the tendons can be detensioned, inspected and retensioned readily during the life of l the plant. The vertical cylinder wall is provided with a system of vertical and horizontal (hoop) tendons.

Vertical tendons are continuous to form inverted U's that extend over the dome. The configuration of the tendons in the dome is based on a three-way system consisting of two groups of vertical tendons oriented ,

at 90 degrees with respect to each other and a horizontal (hoop) group extending from the spring line to approximately 45 degrees from the horizontal. Hoop tendons in both the wall and the dome are placed in l a 240 degree system in which three tendons form two completed rings using three buttresses for  !

anchoring the tendons. Each tendon is comprised of a maximum of 170 - 1/4 inch wires, terminating at i each end with a cold formed buttonhead at the anchorage fixture. l Page 1 of 3 I

f SPECIAL REPORT 99-01 The essential criterion for operability of the tendon system is to maintain the required prestressing force over the life of the plant. This prestressing force for an individual tendon is commonly referred to as the

" lift-off" force. Additional characteristics of a tendon are determined by visual examination of a tendon wire l Gnd performing tensile testing of a wire. An individual tendon has a maximum of 170,1/4 inch diameter I wires. This number of wires provides a redundant system so that a defect in an individual wire l will not compromise the strength of the entire tendon. i DISCUSSION OF FILLER MATERIAL  !

The essential criterion for the operability of the sheathing filler materialis to prevent corrosion of both the 1 tendon wires and the anchorage components. The material used in the Callaway Plant post-tensioning  !

system, Visconorust 2090P-4, accomplishes this by a characteristic which gives the filler grease an affinity to adhere to steel surfaces, an ability to emulsify any moisture in the system which nullifies its rusting tendency, and resistance to moisture, mild acids and alkalis. In addition, protection is afforded by each  !

tendon wire being individually pre-coated with a grease, Amber 1601, prior to initial installation.

Previous surveillance results indicate that grease voids do not affect the corrosion inhibiting properties of the grease. From tensile tests on the removed wires and from visualinspections of the filler grease and tendon components, the filler grease is performing its intended function of prohibiting or arresting corrosion of the tendons.

The void in the tendon sheathing, as indicated by the refill volume varying from 5.7% to 6.0%, may be attributed to a number of factors, )j 1

1) Visconorust 2090P-4 has a coefficient of expansion which yields an expansion of about 1%

per every 20*F. Initial filling temperatures of the filler grease averaged 160*F. Cold weather i conditions can cool the filler material to 40 F, giving a contraction of 6% of the net duct volume. During the fifteenth year inservice surveillance of the tendons, the temperature of insitu filler grease averaged 80*F, giving a contraction of approximately 4% from initial fill.

2) Characteristics of the initial filling method may induce air entrapment into the filler grease. I Pumping operations can introduce air into filler material and may add up to as much as 2% of the net duct volume. The tendons at Callaway Plant were initially greased between April and l October,1981 by Inryco using current industry standard filling procedures.

3) Calculated voids between the wires that compromise the tendon bundle are approximately 7%

of the net duct volume. During the initial filling operations, the tendon bundle was cold (ambient temperature of 65'F) and as the heated filler grease (exit temperature of 140 F) was pumped into the sheathing void, it solidified on the surface of the tendon bundle, leaving small voids between the wires. As the filler grease gradually heated the tendon bundle, it is possible that thf voids between the wires allowed migration of the filter grease into the tendon bundle. Because this process is slow and gradual, it is reasonable to expect that it took place substantially after the filling operation was complete and possibly during the surveillance refill operation. In addition, this type of migration could also occur at other areas such as where tendons are in contact with the sheathing.

In addition, visual inspection of the exterior concrete of the containment building and grease caps after the

. initial greasing and duri1g the surveillance revealed very minor amounts of grease seepage from the tendon grease caps. Therefore, refill volumes in excess of the lost grease during the surveillance indicates that the void existed within the tendon duct boundary.

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SPECIAL REPORT 99-01 The Callaway Plant tendons requiring net refill volume of the filler material in excess of the 5% criteria have not shown any abnormal visual deterioration. The lift-off force for those tendons was found to fall .

within or above the predicted limits. Visualinspection of the different components of the anchorage I system and a wire removed from tendon 40CB revealed proper coverage by the filler material with no l signs of corrosion or presence of water. j i

CONCLUSIONS As indicated above, the function of the filler grease protecting the post-tensioning system was maintained.

As long as sufficient filler grease has been introduced into the system to coat the tendon wire bundle and anchorage system, corrosion protection is assured. Voids can be expected due to the characteristics of the filler grease and initial filling operations as noted above. Since each wire is individually pre-coated )

with Amber 1601, the degree of filling interstitial spaces, which comprise the net duct volume, is not directly related to the degree of coating which occurs, and therefore, is not a major indicator of the operability of the post-tensioning system. Based on the lift-off results, visualinspection, and results from the first, third, fifth, tenth, and fifteenth year surveillances, we have concluded that the structural integrity of the tendon and anchorage system has not been adversely affected by the measured voids.

l it is concluded that " voids in excess of 5% of the net duct volume" have not resulted in any degradation of j the post-tensioning system, assuring the structuralintegrity of the containment building structure.

SUMMARY

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The evaluation of measured voids in the tendon sheath demonstrates that the voids have not caused degradation of the post-tensioning system.

Future scheduled surveillances of the post-tensioning system and full pressure integrated leak rate tests will monitor the structural parameters of the containment to detect any pctential abnormal degradation, assure continued operability of the system, and verify containment building structuralintegrity.

This report has been filed to meet the 30-day Action Statement as specified in the FSAR Section I 16.6.1.2.b.

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